Quality mounts: all mounts are granted unique abilities/traits and all can be customized with different piece of armours/equipment.

Chocobo: Jack-of-all-trades mount. Can equip the widest variety of equipment and has a big set of abilities. Chocobo can become the fastest mount.

Goobbue: Combat mount. Can equip only a few pieces of equipment. Examples of Goobbue abilities/traits: higher defence, intimidation (less chances of being engaged by free roaming monsters), more HP (they are really big after all), etc.

Magitek Armour: Best combat mount. Can be upgraded with different equipment but for a price. Lots of combat abilities, moves and traits. Could also have speed penalty or something like that for balance.

etc.

If it's mounts just to have mounts (like WoW), it gets less interesting.